Method of forming phosphate coatings on drawn wire



atent 2,875,1ll Patented Feb. 24, 195$ METHDD F FORMING PHOSPHATE COATINGS ON DRAWN WIRE Cyril Frank Wilkinson, Winsford, Herbert Arthur Henry Jenkins, West Acton, London, Leslie Thomas Lake, Hounslow, and Stanley V. Radcliffe, 'Bebington, Wirral, England, assignors to Parker Rust Proof Company, Detroit, Mich., a corporation of Michigan .No Drawing. Application December 6, 1954 Serial No. 473,438

8 Claims. (Cl. 148 -615) The usual method of forming a phosphate coating on wire is to immerse a coilof wire in a hot aqueous acidic phosphate solution which is capable of coating that wire for a period of. usually 5-10 minutes. Coatings produced by this method are generally not uniform and con: tain bare patches due to the contact and the overlapping of the wire at theturns, thebare patches being especially noticeablein the middlelof the coils. In many cases :the penetration of the solution to the middle of the coils is insufficient to produce a satisfactory coating. In wire drawing plants where the wire passes continuously in an axial direction through a heat treating or annealing furnace and subsequently to the drawing dies, no satisfactory process for continuously forming a protective phosphate coating on such travellingwire has been heretofore known.

It is the primary object of this invention to provide a process which forms a satisfactory protective phosphate coating on wire traveling at speeds normally encountered inwire drawing plants.

In accordance with this invention ithas been found, surprisingly, that phosphate coatings can be formed on traveling wires or strips by an immersion process in which the wire is immersed in the coating solution for only a short period of time. The method of the present invention comprises the steps of patenting or close annealing the wire to be coated, pickling the annealed wire if necessary, passing the cleaned annealed wire through an accelerated aqueous acidic phosphate coating solution having a pointage greater than 30, the speed of travel andthe duration of immersion of the wire or strip in the solution being so correlated with the degree of acceleration of the solution that the initial formation of the coating occurs in the solution with care being taken that the wire or strip emerges from the solution carrying a uniforin film of the coatingsolution on the surface of the Wire. The final formation of the protective phosphate coating occurs after the wire leaves the coating solution and in certain cases where the time is short between the instant the wire emerges 'from the coating solutions and its entrance into a lubricating solution or the drawing dies it is necessary to apply heat to the film on the wire surface to assist and accelerate thecompletion of the formation of the phosphate coating. In conventional aque- .Ous acidic phosphate coating solutions the pointage employed is usually about 20 although higher percentages up to about 40 are sometimes employed for certain applications. As used in this specification and in the appended claims, the term pointage means the number of ccs. of N/lONaOH required to neutralize 10 ccs. of the coating solution when phenolphthalein is employed as the endpoint indicator. Whereas times of 5-l0 minutesare usually employed in accelerated acidic phosphate solutions for coating metal by immersion and shorter times of about one minute are employed with similar solutions applied by spraying, the unusual and surprising result obtained by the present invention is the formation of high quality phosphate coatings-in extremely short periodsof time such as /8 to /2 minute. Although the reason for the formation of phosphate coatings on the traveling wire is not fully andcompletely understood, it is believed that the combination of factors of providing an. annealed Wire surface which is in a chemically cleaned condition to gether with the high speed of relative motion between the coating solution and the surface being coated is responsible for the formation of the coating.

The present invention is applicable to wire or strip made from ferrous metals, zinc, cadmium or aluminum.

As employed in this specification and in the appended claims by the term patenting or close annealing is meant that wire or strip is heated to a temperature above the transformation range of the metal in question and allowed to cool in an inert non-oxidizing atmosphere. This heat treatment anneals the metal to a soft condition while concurrently preserving the surface in a substantially chemically clean condition. Where the close annealing atmosphere is not completely non-oxidizing and the surface of the Wire or strip to be drawn contains traces of oxide, the wire or strip should be pickled to insure that the surface of the wire or strip is chemically clean when it comes into contact with the phosphate coating solution.

It has been found that the most satisfactory coatings are formed from solutions which contain only a moderate amount of ingredients which produce acceleration. If the degree of acceleration is too high, large amounts of the products of decomposition of the accelerator are left in or on the coating and the coating contains insufficient metallic phosphate to give the desired quality of final formed phosphate coating. Coatings formed from solutions containing too much accelerator are usually covered with granular white solution or dust. Where the degree of acceleration of the solution is: too low the fully treated Wire is coated with an amorphous, often bluish film instead of the desired crystalline phosphate coating. It is therefore preferred that the degree of accelerator present in the solution be controlled so that the resultant coating is of the crystalline-phosphate type and free from excessive quantities of accelerator decomposition products. The phosphate coating solutions of this invention may contain any of the now well-known accelerating agents and the control of the quantities of such accelerating agents to produce the above desired type of coating is considered to be Well within the capabilities of one skilled in this art. For most purposes a chlorate accelerator or a mixture ofa chlorate and a nitrate as the accelerator is preferred. Where chlorate and nitrate are present it has been found that the best results are ob- V tained when the ratio of the sum of chlorate and nitrate to P0 lies between 0.1 and 0.6. In most instances in the continuous production of wire, the wire or strip being coated travels at a speed of at least feet per minute through such solutions and at such speeds the high quality protective phosphate coatings of this invention are formed. Speeds of wire traveling up to about 60 feet per minute have been successfully employed and even greater speeds may be used where the length of the phosphate coating solution tank, the pointage of the coating solution and the total immersion time are properly correlated andcontrolled.

After the phosphate coating of this invention is completely formed on the surface of the traveling wire or strip, it is advantageous to further coat the wire with a suitable drawing lubricant prior to the actual drawing operation. The phosphate coated wire may be coated with borax or lime and thereafter coated with a drawing soap in dry or liquid form. Any of the now well-known formulations of drawing soaps may be satisfactorily employed. The coating of lime or borax may be applied by coiling the Wire carrying the phosphate coating and thereafter immersing the coil in a suspension of lime or in a solution of borax or by continuously passing the phosphate coated wire through a suitable lime or borax bath. In the event the phosphate coated wire is to be stored prior to being drawn, it is desirable to rinse the coated wire in cold water immediately after the phosphate coating step. Where the phosphate coated wire is to be stored for extended periods of time it is desirable to apply the selected drawing lubricant before storage, especially good resistance to corrosion being obtained when the drawing lubricant is modified to contain a small quantity of about .05 %-.15 by weight of an inhibitor selected from sodium nitrite, sodium chromate and sodium benzoate in about a 2% solution by weight of the water-soluble drawing soap. When wire or strip is coated without employing heat after the wire emerges from the coating solution the pointage of the phosphate solution is preferably maintained above 40 and is most advantageously maintained between 60 and 80. Satisfactory coatings can be formed in such solutions in not more than seconds when the wire or strip passes through the solution at a speed of at least about 50 feet per minute.

In completely processing wire or strip in accordance with the method of this invention, wire may be passed continuously in an axial direction at a speed of, for example, 60 feet per minute through a close annealing furnace, a pickling solution or other mechanical scrubbing device, if needed, and then through a phosphate coating solution of the accelerated type above described, then coated with lime, borax and/or a drawing soap. A suitable pickling solution may consist, for example, of a cold 10% solution of hydrochloric acid in which the wire may remain for about a second or so. The phosphate bath is disposed preferably in a long narrow container so arranged that the wire remains in the solution for 7-10 seconds. The wire may then be rinsed, if desired and passed through a lime or borax solution for about a second. The wire may then be dried in air or in a furnace and coated with the selected drawing lubricant as desired. It may be necessary to apply additional heat to the wire as it emerges from the phosphate solution carrying a retained film of the solution on the surface. Even in instances where there is no limitation on phosphate coating solution tank length, it may be necessary to apply supplemental heat where the metal being coated is relatively more difficult to coat. Even where the speed of travel of the wire through the drawing plant is such that heating is required to complete the coating formation on the surface of the wire, it is desirable to regulate the pointage of the solution so that crystal nuclei are formed on the wire surface before it is removed from the solution. It is also important to make sure that the fi'm of phosphate coating solution adhering to the wire as the wire emerges from the solution is uniform over the surface of the wire. The supplemental heating may be accomplished by the use of a gas flame, high frequency induction coils or by passing the wire through a furnace. During this heating step strong oxidizing or strong reducing conditions should be avoided. When the wire is to be subsequently heated it is preferred that the pointage of the phosphate coating solution be maintained between 50 and 70. The phosphate coating solution may be any of the now well-known coating solutions which produces a phosphate coating containing the metal ion from the coating solution itself such as, for example, zinc phosphate, manganese phosphate, iron phosphate and cadmium phosphate. The.

selected phosphate coating solution should be maintained at or near its equilibrium temperature, preferably in the range of about -180 F. Zinc phosphate coating solutions have been found to be the most desirable solutions to operate from all standpoints and for this reason are preferred.

In drawing wire the weight of the phosphate coating on the surface which is required varies somewhat with the type of wire and the conditions employed during the drawing operation. In general, coatings weighing about 700 mg./sq. ft. are suitable although weights as low as 250 mg./sq. ft. or as high as 1000 mg./sq. ft. may be used satisfactorily. If desired, the coating weight can be increased by the addition of 0.1% to 0.2% by weight of an a-amino polycarboxylic acid or 0.02% to 0.08% by weight of a soluble copper salt.

It will be apparent to those skilled in the art that the weight of the coating desired on different types of metals and for varying conditions of drawing may be varied by adjusting the time of immersion of the wire or strip in the phosphate coating solution, by adjustment of the strength of the solution and by heating the wire or strip if necessary. Heating the wire or strip carrying a film of solution increases the weight of the coating on the wire surface.

One of the important advantages of the process of this invention is that the chemical consumption for the formation of a coating of a given weight is lower than that normally encountered, and the process is therefore more eflicient than conventional processes.

Drag-out is limited to the uniform film of solution which adheres to the surface of the wire as it leaves the solution at a uniform rate. This drag-out is to be contrasted to the larger volumes of phosphate coating solution which are trapped in the coil of wire or strip as they are rapidly withdrawn from the solution in the coiled wire batch-type of operation. The higher eificiency is in part accounted for by the fact that the amount of phosphate coating solution which adheres to the surface of the wire emerging from the coating solution is regulated to be only that amount which is necessary to complete the formation of the desired coating. I The examples given below will illustrate this invention in greater detail. While the specific examples employ zinc phosphate, manganese, iron and cadmium phosphates in comparable strengths work equally satisfactorily.

Example I A phosphate coating solution was prepared having the following composition, percentages being expressed as weight over volume, that is, the specific gravity of the solution is one.

This solution was determined to have a pointage of 80 as determined by the above specified procedure and was heated to and maintained at a temperature between F. and F. Two batches of steel wire of 0.039" diamtiter and containing approximately 0.65% carbon were Y J u i 5 treated by passing the wire in series through a patenting or close annealing furnace at 900 C., and having an atmosphere of flue gases and then cooling the wire in that atmosphere to 200 C., passing the wire into the above phosphate coating solution at a speed of 60 feet per minute such that it remained in the solution for 13 seconds, passing the wire through the flame of a Bunsen burner after the wire emerged from the coating solution and until the wire was dry. The wire was then immediately passed through a solution containing about 5% borax and dried by passing over a steam coil. The coated wire was then wet-drawn at finishing speeds of 2000 and 2700 ft. per minute respectively in stages to a diameter of 0.0164. The drawing characteristics of both batches of wire were equally as good as if the wire had been emerged in the form of coils in the same bath for from 5-10 minutes.

Example 11 In this example the phosphate solution was the same as in Example I.

0.5% carbon wire was patented as in Example I, pickled in cold hydrochloric acid and passed through grit over which water was flowing to remove carbonaceous matter. It was then rinsed in water and passed through the phosphate solution with the actual time of immersion being 11 seconds. The wire was allowed to dry in air for 6 seconds, water-rinsed and passed into a boiling borax solution. It was then dried in an oven and reeled. Two batches of this wire which had a diameter of 0.036 inch were then satisfactorily continuously wet-drawn through ten holes at 2,700 feet per minute to diameters of 0.0124 and 0.0092 inch respectively.

Example III A stock solution was prepared by adding 120 grams of zinc oxide, 375 grams of phosphoric acid to 1000 grams of water. Seventy (70) grams of this stock solution was diluted to 1 liter and 0.5 gram of sodium nitrophenol sulphonate was then added. This produced a 40 point solution. Steel strip which had been close-annealed was pickled in a 10% solution of hydrochloric acid and then treated in this solution for 10 seconds and then heated as in Example I. A satisfactory, very finely crystalline coating was produced.

Example IV A stock solution was prepared from 725 grams of zinc oxide, 730 grams of nitric acid of specific gravity 42 B., 2,400 grams of 75% phosphoric acid and water to make a total weight of 5,400 grams. 70 grams of this stock solution was diluted to 1 liter and 0.15 gram of sodium nitrite was added. The solution had a pointage of 40. Steel wire was patented and treated in this solution at 160 F. for 10 seconds and then heated. The wire had a rather thin crystalline coating, but this facilitated colddrawing of the wire.

Example V A coating solution was made up by adding 40 grams zinc primary phosphate and 5 grams of nitro-guanidine to 1000 grams of water. The solution had a pointage of 40. Steel wire was patented and immersed in this solution in the cold for seconds and then heated as in Example I. Coatings were produced which were used to facilitate the cold-drawing of the wire.

Example VI A steel rod having a diameter of 0.212 inch was passed through a patenting furnace and then through the solution used in Example I at a speed of 12 feet per minute, the rod remaining in the solution for 30 seconds. The rod was then rinsed and coated with lime.

After the application of a drawing soap the rod was dry drawn to a diameter of 0.08 inch through 6 holes finishing at 700 feet per minute.

What is claimed is: i i

1. A method of forming a phosphate coating on wire which comprises the steps. of passing the wire in a chemically clean condition, continuouslyin an axialdirection through an aqueous acidic accelerated phosphate coating solution selected from the group consisting of zinc, manganese, iron and cadmium phosphate solutions and having a pointage greater than about 40 and containing an accelerator selected from the group consisting of nitrite, nitrophenol, nitroguanidine, a mixture of chlorate and nitrate and a mixture of nitrite and nitrate, the ratio to phosphate of said accelerator being in the range of 0.0075 to 0.6, regulating the speed of travel and the duration of immersion of the wire in the solutionwith the degree of acceleration so that the initial formation of the coating occurs in the coating solution and the wire emerges from the coating solution carrying a uniform film of the solution on its surface, which film serves to complete the formation of the phosphate coating on the surface of the wire.

2. A method of forming a phosphate coating on wire which comprises the steps of close annealing the wire, pickling theannealed wire, passing the wire continuously in an axial direction through an accelerated phosphate coating solution selected from the group consisting of zinc, manganese, iron and cadmium phosphate solutions and having a pointage greater than about 40 and containing an accelerator selected from the group consisting of nitrite, nitrophenol, nitroguanidine, a mixture of chlorate and nitrate and a mixture of nitrite and nitrate, the ratio to phosphate of said accelerator being in the range of 0.0075 to 0.6, regulating the speed of travel and the duration of immersion of the wire in the said coating solution with the degree of acceleration of the said solution so that the initial formation of the coating takes place in the solution and the wire emerges from the solution carrying a uniform film of the coating solution on its surface, heating the wire after it emerges from the coating solution to complete the formation of the coating, said coating being crystalline and substantially free from products of decomposition of the accelerator.

3. A method for forming a phosphate coating on the surface of wire which comprises the steps of close annealing the wire, passing the annealed wire continuously in an axial direction at a speed of at least 10 feet/minute through an aqueous acidic dihydrogen phosphate coating solution selected from the group consisting of zinc, manganese, iron and cadmium phosphate solutions and having a pointage in the range of about 50 to about and containing a mixture of chlorate and nitrate accelerator, the ratio of the sum of the chlorate and nitrate to the phosphate being between 0.1 and 0.6.

4. A method in accordance with claim 3 wherein the phosphate coated wire is heated after it emerges from the phosphate coating solution.

5. A method in accordance with claim 3 wherein the duration of immersion of the wire in a phosphate coating solution is not more than 15 seconds.

6. A method for drawing wire which comprises the steps of close annealing the wire, passing the annealed wire continuously in an axial direction at a speed of at least 10 feet per minute through an aqueous acidic dihydrogen phosphate coating solution selected from the group consisting of zinc, manganese, iron and cadmium phosphate solutions and having a pointage greater than about 40 and containing an accelerator selected from the group consisting of nitrite, nitrophenol, nitroguanidine, a mixture of chlorate and nitrate and a mixture of nitrite and nitrate, the ratio to phosphate of said accelerator being in the range of 0.0075 to 0.6 coating the wire with a drawing lubricant and thereafter drawing the lubricated wire.

7. A method in accordance with claim I wherein the pointage of said solution is between 60 and. 80 and the 7 speed of the said wire in the solution isat least about 2,487,137 50 feet/minute. 1 2,499,261

8. A method in accordance with claim 2 wherein the pointage of said solution is between 50 and 70 and said coating has a weight between 250 mg./ sq. ft. and 1000 5 517,049

' References Cited in the file of this patent 706, 714,321

UNITED STATES PATENTS 1,910,385 Fisher et a1 May 23, 1933 10 8 Hoover et a1. Nov. 8, 1949 Rosenbloom Feb. 28, 1950 FOREIGN PATENTS Great Britain J an. 18, 1940 Great Britain June 21, 1949 Great Britain Mar. 31, 1954 Great Britain Aug. 25, 1954 

1. A METHOD OF FORMING A PHOSHATE COATING ON WIRE WHICH COMPRISES THE STEPS OF PASSING THE WORE IN A CHEMICALLY CLEAN CONDITION, CONTINUOUSLY IN AN AXIAL DIRECTION THROUGH AN AQUEOUS ACIDIC ACCELERATED PHOSPHATE COATING SOLUTION SELECTED FROM THE GROUP CONSISTING OF ZINC, MANGANESE, IRON AND CADMIUM PHOSPHATE SOLUTIONS AND HAVING A POINTAGE GREATER THAN ABOUT 40 AND CONTAINING AN ACCELERATOR SELECTED FROM THE GROUP CONSISTING OF NITRITE, NITROPHENOL, NITROGUANIDINE, A MIXTURE OF CHLORATE AND NITRATE AND A MIXTURE OF NITRITE AND NITRATE, THE RATIO TO PHOSPHATE OF SAID ACCELERATOR BEING IN THE RANGE OF 0.0075 TO 0.6. REGULATING THE SPEED OF TRAVEL AND THE DURATION OF IMMERSION OF THE WIRE IN THE SOLUTION WITH THE DEGREE OF ACCELERATION SO THAT THE INITIAL FORMATION OF THE COATING OCCURS IN THE COATING SOLUTION AND THE WIRE EMERGES FROM THE COATING SOLUTION CARRYING A UNIFORM FILM OF THE SOLUTION ON ITS SURFACE, WHICH FILM SERVES TO COMPLETE THE FORMATION OF THE PHOSPHATE COATING ON THE SURFACE OF THE WIRE. 